1. Field of the Invention
The present invention generally relates to digital receivers, and more specifically to digital receivers capable of processing both analog and digital signals.
2. Background Art
Television signals are transmitted at radio frequencies (RF) using terrestrial, cable, or satellite transmission schemes. Terrestrial and cable TV signals are typically transmitted at frequencies of approximately 57 to 860 MHZ, with 6 MHZ channel spacing in the United States and 8 MHz channel spacing in Europe. Satellite TV signals are typically transmitted at frequencies of approximately 980 to 2180 MHz.
Regardless of the transmission scheme, a tuner is utilized to select and down-convert a desired channel from the TV signal to an intermediate frequency (IF) signal or a baseband signal, which is suitable for processing and display on a TV or computer screen. The tuner should provide sufficient image rejection and channel selection during down-conversion as is necessary for the specific application. The National Television Standards Committee (NTSC) sets standards for television signal transmission, reception, and display. To process a NTSC signal, it is preferable that the tuner have a high-level of image rejection. However, less image rejection is acceptable for non-NTSC signals depending on the specific application and the corresponding display requirements.
After the tuner down-converts the desired channel from the TV signal, the resulting IF or baseband signal is typically converted into a digital signal to be processed by a digital receiver. However, placing an analog signal, such as the desired channel from the TV signal, in close proximity with a digital signal can cause interference between the signals. Thus, the tuner circuitry and the digital receiver circuitry are often separated in traditional communication systems.
Separating the tuner circuitry and the digital receiver circuitry has several disadvantages. For example, more circuit area is needed for separate tuner and digital circuits, which leads to higher cost.
What is needed is a method or apparatus for integrating tuner functions in a digital receiver.